Hi,
Ok, that's slightly different, since you are not showing the Target object in front of you but only want the true north.
- take the y rotation of the your camera, this is a direct relation with the north. Let's assume that when y rotation is 0, this is north. this will do as a first step, then you'll want the world rotation, not the local rotation.
- remap this angle to translate the image of your compass.
Let me know how you progress on this.
Bye,
Jean